1. Field of the Invention
The present invention relates to a data transmission system, a receiver, and a recording medium for use in data transmission and data reception applications for various kinds of data such as characters, image data and so on, and, more particularly, to a data transmission system, a data receiver, and a recording medium, that are capable of improving a data error rate of the data transmission, for use in data transmission using radio transmission channels or paths such as automobile telephones and the like.
2. Description of the Prior Art
FIG. 18 is a block diagram showing a configuration of a received data extraction section in a conventional receiver that has been disclosed in the literature "Digital communication", John G. Proakis, Second edition, McGraw-Hill, 1989. In FIG. 18, the reference number 201 designates a modulator for performing decision of received signal and for outputting a hard-decision value or a soft-decision value. The reference number 202 denotes a deinterleaver for alining outputs from the demodulator 201 into an original data sequence. The reference number 203 indicates a decoder for decoding coded data outputted from the deinterleaver 202. The received data extraction section described above receives the transmission signals through radio transmission channels or paths, an antenna, a band filter, and an A/D converter, for example.
The conventional receiver including the received data extraction section having the above configuration is combined with a transmitter having a transmission signal generator shown in FIG. 19 so as to form a data transmission system. In FIG. 19, the reference number 211 designates a coder for coding the transmission data, 212 denotes an interleaver for arranging the coded data outputted from the coder 211, and 213 indicates a modulator for generating transmission signals that have been modulated by using the arranged data.
Next, a description will be given of the operation of the conventional data transmission system.
In the transmitter, the coder 211 performs coding of the transmission data, the interleaver 212 arranges the coded data sequence, and the modulator 213 modulates the arranged data sequence and transmits the modulated data as transmission signals.
On the other hand, in the receiver, the demodulator 201 performs decision processing for the received signals and outputs a hard-decision data or a soft-decision data as a decision result, the deinterleaver 202 arranges the output from the demodulator 201 into the original data sequence, the decoder 203 decodes the coded data outputted from the deinterleaver 202 and then outputs the received data.
The above coding processing is a redundancy processing for data so as to perform error correction processing to be executed by the receiver side.
The hard-decision processing is a processing to perform the decision processing of the kind of the transmitted data, and to output transmission data sequence after the hard-decision processing as the hard-decision data. Therefore when the transmission data sequence are made up of two-value signals such as 1 and -1, the data sequence formed by the combination of the two-value signals 1 and -1 are outputted as the hard-decision data.
On the other hand, the soft-decision processing is a processing to perform a decision of a reliability data of the hard-decision processing with the hard-decision data. Therefore when the transmission data sequence are made up of the two-value signals such as 1 and -1, various data items such as +30 (data +1 has a higher reliability), +0.9 (data +1 has a lower reliability), -0.4 (data -1 has a lower reliability), and -50 (data -1 has a higher reliability) are outputted.
In the above example, a code or sign of the soft-decision value represents the hard-decision value in which the hard-decision value becomes 1 when the sign is Plus "+", and the hard-decision value becomes -1 when the sign is Minus "-", and the absolute value of the soft-decision value represents the reliability. In this case, when the magnitude of the absolute value is larger, the reliability is increased. In general, it is generally known that utilization of the soft-decision processing has a lower error rate at the output of the decoder than utilization of the hard-decision processing.
A maximum-likelihood sequence estimator of digital sequence and soft-decision output equalizer may be used as the above demodulator 201. This maximum-likelihood sequence estimator of digital sequence has been disclosed in the literature "Maxmum-likelihood sequence estimation of digital sequence in presence of intersymbol interference", G. D. Forney, Jr., IEEE Trans. Information Theory, vol.IT-18, pp.363-378, May 1972. The soft-decision output equalizer have been written in the literature "Optimum and sub-optimum detection of coded data disturbed by time-varying intersymbol interference", W.Koch, IEEE GLOBECOM '90, San Diego, pp.1679-1685, December 1990.
Further, a data demodulation method may also be used as the demodulator 201. This data demodulation method has been disclosed in the literature "A MLSE receiver for the GSM digital cellular system", S. Ono. IEEE 44th, VTC, Stockholm, pp.230-233, June 1994. In the data demodulation method described above, the soft-decision data is calculated and outputted based on the hard-decision data outputted by the maximum-likelihood sequence estimator.
Because the conventional data transmission system has the configuration described above, when it is constructed by using the radio transmission channels or paths for automobile telephones and the like in which burst errors relatively happen, the data error rate becomes higher relatively, so that it causes a drawback that it is difficult to have a better quality.